The multi-channel development system used in electrophotographic printers has a development roller that moves developer containing marking particles (toner) into proximity with a primary imaging member, usually a photoconductor; and a first channel containing a feed auger, a second channel containing a mixing auger, and a third channel containing a return auger. The primary imaging member is used for forming an electrostatic image. The developer used in development systems of this type usually contains magnetic carrier particles and marking particles. The marking particles are removed from the development system to form an image on the primary imaging member.
The flow of developer through the three channel development system is such that developer is fed from the second channel to a first end of the feed auger in the first channel. As the developer travels longitudinally down the length of the feed auger, a portion of the developer is fed transversely from the feed auger to the development roller to produce a layer of developer on the development roller. The remainder of developer in the first channel continues to travel longitudinally down the length of the feed auger.
To produce a uniform image, the layer of developer on the development roller should be homogeneous and uniform along its length. The developer that is fed onto the development roller should contain marking particles that are at a constant concentration and have a uniform and narrowly distributed charge level. The developer that is fed to the development roller moves over the development roller and is not returned to the feed auger but instead drops into the return auger in the third channel. The used developer in the third channel has a toner concentration that is not uniform and is dependent on the image content of the image on the primary imaging member.
Developer moves longitudinally in the same direction in both the first channel and the third channel, from the first end of the augers to the second end, which is at the rear of the development system. At the rear of the development system, the developer collected by the third channel and the remaining developer in the first channel are both transported into the second channel. It is also at this point that replenishment marking particles are added to the developer to replace the marking particles that have been applied to the primary imaging member. The developer is moved longitudinally along the second channel by the mixing auger toward the first end of the feed auger. The developer that has traveled the length of the second channel is fed to the first end of the feed auger in the first channel, so that the developer is cycled continuously from the first channel to the development roller, from the development roller to the third channel, from the first and third channels to the second channel, and from the second channel to the first channel while the development system is running.
The mixing auger in the second channel needs to perform at least two functions. One function is to transport the developer that was collected from the second end of the first channel and second end of the third channel to the first end of the first channel. A second task is to mix the developer so that the developer that is delivered to the feed auger in the first channel is homogenous in marking particle concentration and marking particle charge. The developer that enters the second channel at the rear of the development system is a mixture of used developer from the third channel and the remaining developer that has traveled the length of the first channel. These two developer streams enter the second channel at the rear of the development system and it is at this point that replenishment marking particles are added. The used developer from the third channel, the unused developer from the first channel, and the replenishment marking particles need to be well mixed so that a homogeneous developer is presented to the first end of the feed auger, thus enabling the production of uniform, high-quality images. It is advantageous to have a means of thoroughly mixing the developer in the second channel while maintaining the necessary transport function of the mixing auger so that a homogeneous and steady supply of developer is provided to the first channel and the development roller.